My Right Knee Has Been Hurting For 2 Months. I

My right knee has been hurting for 2 months. I have been walking an average of 6 miles a day for a couple years. Not sure how I injured it. It hurts on the outer side of the knee in the back. Hurts when it twist. Hurts more walking downstairs than upstairs. Have iced it and adviled it. However, when it seems better I start walking and it goes right back to hurting. Torn miniscus? Can I ride a bike in the mean time?